A wide variety of insulating barriers has been proposed in the art for abating sound transmission from a source thereof to some protected area or enclosure. Notable examples of such sound barriers are those used for abating sound through walls of houses, buildings and the like, those used for abating sounds emanating from highways and expressways, those used for abating sounds from appliances, such as washing machines, dishwashers and the like, and those used for abating sounds from the exterior of an automobile to the interior of the automobile. The sounds to be abated vary considerably with the sources of the sounds, and such sounds can have quite wide frequency ranges, commencing with only a few Hertz up to thousands of Hertz. Thus, for every sound abatement application, it is necessary to provide an acoustical insulating barrier which is effective at the frequencies expected from the sound to be abated. For example, the usual sounds transmitted from the exterior of an automobile to the interior thereof generally have frequencies from about 20 to 400 Hz. These sounds are generated by tire and road noise, engine noise, wind noise, noise from flexing of the automobile chassis or body, and noise from vibrations of movable and static mechanical components.
Accordingly, considerable effort has been expended in the art to provide acoustical insulating barriers which are effective in that frequency range, so that sound abatement can be provided to the interior of an automobile or like vehicle, although such acoustical insulating barriers are useful in other applications, such as dishwashers, washing machines, dryers, furnaces and like appliances. It has been found that sounds in those frequencies and up to frequencies of approximately 1000 Hz, and for some purposes up to 2000 Hz, are more effectively abated by use of a high density material which is, ideally, not in physical contact with the source of the sound or an object which transmits the sound. For example, the interior of an automobile is routinely acoustically insulated from sound transmitted through the floorboard, which sound originates from tires and road noises, wind noises, engine noises, and noise from vibration of mechanical and structural parts of the automobile. To isolate the acoustical barrier from that transmitting floorboard, to the extent possible, it is a common practice in the art to provide a fibrous material between the sound barrier and the floorboard. This material dampens sound transmissions and mechanical vibrations which would otherwise be transmitted directly to and through the acoustical insulating barrier. Thus, direct physical contact of the sound barrier is avoided by such material which spaces the acoustical insulating barrier from the floorboard. A wide variety of such materials has been used in the art, including non-woven textile fabrics, particularly "shoddy" fabrics, foamed polymeric materials, and the like. These materials are referred to in the art as a "suspending layer".
Very typically, the high-density acoustical insulating material is in the form of a layer of synthetic material (sometimes referred to as "mastic"). That synthetic material can take various forms, but typically will be made of a bituminous material or a bituminous/rubber material or a polymeric material which is either dense in and of itself and/or has added thereto densifying materials in order to be more effective in the relevant frequencies.
Typically, the acoustical insulating barrier layer (mastic) is glued to the suspending layer so that a composite is formed of the insulating barrier layer and suspending layer. In the case of an automobile, for example, that composite acoustical insulating barrier is placed under the cabin carpet of the automobile, although it may also be placed under the felt or carpet used in the trunk of the automobile or between the trunk liner and the body of the automobile or between the head liner and the roof of the automobile.
However, in each such application, in modern automobile production, the automobile manufacturers usually require that the supplier of the carpet, trunk floor felt, etc., provide those units in a ready-to-be-installed form. This means that each of the units, for example, the carpet covering the floorboard in front of the driver and front passenger seat, has been molded to the general configuration of that portion of the floorboard and the acoustical barrier has been attached thereto. This simplifies the assembly of the automobile, in that the carpet and acoustical insulating barrier can be quickly placed on the floorboard of the automobile during assembly, and it will snugly fit the contours of that portion of the floorboard. Hence, little time is required in installing that portion of the carpet/acoustical insulating barrier assembly.
In view of the foregoing, typically, a supplier of the carpet for the automobile will adhesively bond the acoustical insulating barrier, consisting of the barrier layer and suspending layer, to the underside of the carpet and then mold that assembly into the generally required configuration, as explained above.
Since the acoustical insulating barrier layer is glued to the suspending layer and the acoustical insulating barrier layer is, in turn, glued to the underside of the carpet, two different glue lines are required for that assembly, with one glue line being applied by the manufacturer of the acoustical insulating barrier and another glue line being applied by the manufacturer of the assembly of the carpet and the acoustical insulating barrier.
Since all conventional glues of this nature contain some fugitive component, e.g. solvent, for environmental purposes, containment systems must be provided both in the manufacture of the acoustical insulating barrier and in the manufacture of the assembly of acoustical insulating barrier and carpet. This significantly increases the cost of both of the acoustical insulating barrier and the assembled acoustical insulating barrier and carpet.
In addition, since the prior art acoustical insulating barrier layers are relatively heavy (typical weights of about 12 to 14 ounces are per square foot), the prior art acoustical insulating barriers made therewith considerably contribute to an increased overall weight of the automobile, which is quite undesirable.
Further, while the glue lines, as explained above, are cured, solvent and other fugitive volatiles, i.e. plasticizers, of the glue used in the glue line cannot be totally removed during manufacture of the acoustical insulating barrier or the assembly of the barrier and the carpet. Those volatiles slowly evaporate from the assembly, after being installed in the automobile, and contribute to the well known film of oily deposit that collects on windshields, glasses, back windshields, door panels and the like, especially, in a new automobile. The automobile manufacturers have, of course, long sought means of reducing that oily film, and the use of such glue lines in the typical acoustical insulating barrier and the assembled barrier and carpet only increase the incidents of the oily film.
As illustrations of the prior art mentioned above, U.S. Pat. No. 4,056,161 to Allen discloses a sound barrier having an outer layer of wear-resistant properties made of a polymer, e.g. polyvinyl chloride, and a sound barrier layer of high-density material filled with particulate material, such as barium sulfate. The sound barrier layer is preferably a vinyl plastisol. In turn, the sound barrier layer is bonded to a suspending layer at its undermost side, which suspending layer is preferably a polyurethane foam. The composite is bound together by heating the composite and allowing the vinyl plastisol of the barrier layer to bond the three layers together. This older product, however, has the disadvantages described above in that the composite assembly is essentially that of an adhesive operation via the vinyl plastisol, and off-gassing of condensable volatiles from that vinyl plastisol can be considerable, which is quite undesired, as noted above.
U.S. Pat. No. 4,966,799 discloses an automobile sound barrier made of fibers and filled with a filler. It is adhesively bonded to a suspending layer and can include a carpet for the automobile. Here again, adhesive bonding of the layers is required.
U.S. Pat. No. 5,266,143 is directed to an automobile sound barrier where a substrate of an elastomer or synthetic rubber, which is filled with a filler, is bonded to a porous fibrous layer by adhesion bonding.
U.S. Pat. No. 5,068,001 describes a sound barrier for automobiles, where a fibrous core is adhesively bonded to fibrous reinforcing mats on each side of the core by way of coating the reinforcing mats with uncured thermosetting resin and molding the composite in a heated mold where the thermosetting resin is cured.
In view of the above-discussed state of the art, it would be a substantial advantage in the art to provide an acoustical insulating barrier which can provide the acoustical insulation of the prior art acoustical insulating barrier, as described above, but which does not require glue for production of the barrier or for the assembly of the barrier and carpet, and, hence, avoid the costly environmental containment required by the barrier manufacturer and the manufacturer of the carpet and barrier assembly, as well as reduce oily volatiles. In addition, it would be a considerable advantage to the art to provide an acoustical insulating barrier which can abate sound as well as the conventional barrier, but with considerably less weight per square unit (lower density) and at a considerably lower cost per square unit.